The present invention relates to an air-conditioning system, and in particular, it relates to an electric power storage air-conditioning system which is able to store surplus electric power during the night-time, when the electric power demand is low, and to use the stored electric power during the day-time, when the electric power demand is high.
Recently, the electric power consumption at the peak-time during day-time use in the summer season has increased enormously, sometimes causing an insufficiency in the available power supply. As one of the countermeasures to cope with such an insufficiency in the power supply, a solar power generation system for generating electric power using solar energy during day-time use has been proposed and development of such systems is in progress. Further, a home-appliance electric power storage system which is capable of storing surplus electric power in a battery during the night-time and retrieving the stored electric power from the battery during the peak-time of the day has been contemplated.
Although, during the peak-time of the day the electric power demand may not be satisfied due to a shortage of the power supply, during the night-time there is surplus of electric power, since most of the factories consuming electric power are not operating at that time. The main cause for the shortage of electric power during the peak-time of the day is caused by the abundance of home-use air-conditioners. As a countermeasure to such a problem, an electric power storage air-conditioner has been proposed, as described in JPA Laid-open No.6-137650. This prior art air-conditioner has a battery and an arrangement for charging its battery from the a.c. side via a control circuit dedicated to the battery and for supplying d.c. power from the battery to the inverter of the air-conditioner.
In the case of a solar power generation system for operating the air-conditioner, a d.c. voltage generated or stored in the battery first must be inverted to an a.c. voltage and then converted to d.c. within the air-conditioner for driving the motor. Therefore, it is inevitable for the system efficiency to decrease substantially.
In the case of a home-use electric power storage system, in the same manner as described above, the d.c. voltage stored in the battery first must be inverted to an a.c. voltage and then converted to a direct current within the air-conditioner for driving the motor. Thus, a drop in the system efficiency cannot be avoided, similar to the above case.
In addition, for the electric power storage air-conditioner disclosed in JPA Laid-Open No.6-137650, a charging control circuit is required which is dedicated for controlling the charging of the battery. This charging control circuit further requires, in addition to a rectifying and smoothing circuit, provision of an active filter circuit for eliminating harmonic currents involved in its a.c. input, which is noted as a problem to be solved. Thereby, as a result of provision of such circuits, the system configuration becomes complicated, large-sized and costly.